Field Evaluation of Citrus Cultivars for Greening Disease Resistance in Thailand

Abstract

Forty-three cultivars of citrus planted in the field at Nan Horticultural Research Station were evaluated for their resistance to greening disease. All the trees were propagated at the Station using Cleopatra mandarin rootstock, and were established in the field in 1986. Most of the scions were free from greening disease when propagated. Field observations in July 1992 revealed that a large number of trees had declined, showing typical symptoms. The cultivars Wilking, Ellendale, Pet-yala, Beauty, Onesco, Pong-chieng-ga (Tankan), Nian-ju, and sweet orange were most susceptible. Many mandarins including Fairchild, Murcott, Kinnow, Clementine, Fremont, Ponkan, King, and Som-keo-wan were next. Queen mandarin, Avon Ever Bearing (calamondin) and rough lemon grew well with mild symptoms. Ladu mandarin and Som-pan mandarin showed the most resistance, with good growth, few symptoms and yielding healthy fruit.